设 $M=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}} \frac{\sin x}{1+x^2} \cos ^4 x \mathrm{~d} x, N=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\left(\sin ^3 x+\cos ^4 x\right) \mathrm{d} x$ ， $P=\int_{-\frac{\pi}{2}}^{\frac{\pi}{2}}\left(x^2 \sin ^3 x-\cos ^4 x\right) \mathrm{d} x$ ，则有
$\text{A.}$ $N < P < M$ ．
$\text{B.}$ $M < P < N$ ．
$\text{C.}$ $N < M < P$ ．
$\text{D.}$ $P < M < N$ ．
$\text{E.}$
$\text{F.}$